Facilities exist to enable power to be transferred from a laptop computer for example, to a mobile phone. For example, battery powered devices such as notebook computers exist which are able to charge smaller mobile devices such as music players, cell phones and PDAs over USB connections. Portable battery powered-devices are becoming increasingly widespread and individuals typically carry many different battery-powered devices with various size, power consumptions and battery capacities. This produces an increasing need to facilitate power transfer and reduce the burden on the end user of managing such power transfer. Power conservation is also a significant issue especially where battery-capacity is limited.
Typically, portable devices with rechargeable power sources often have limited power resources. Often they implement a power conservation process, for example, by automatically powering down when the device is not used for a specified period of time. This is another factor for users to consider when managing power transfer between a laptop for example, and a mobile phone. Existing systems are known which enable a laptop computer to power down for all components except a port which is known to be in use charging a mobile phone. The laptop computer then wakes-up periodically to query the attached mobile device to determine if it has been fully charged.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known devices having power sources.